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          优化7.前沿优化解决方案
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            <div class="post-description">拯救移动端图标 – SVG/Flexbox优化布局；优化资源加载的顺序/预渲染页面；Windowing(窗口化)提高列表性能；使用骨架组件减少布局移动(Layout Shift)</div>

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        <h2 id="拯救移动端图标-SVG"><a href="#拯救移动端图标-SVG" class="headerlink" title="拯救移动端图标 SVG"></a>拯救移动端图标 SVG</h2><h3 id="Iconfont"><a href="#Iconfont" class="headerlink" title="Iconfont"></a>Iconfont</h3><blockquote>
<p><a target="_blank" rel="noopener" href="https://www.iconfont.cn/">iconfont</a></p>
<p><a target="_blank" rel="noopener" href="https://icofont.com/">icofont</a></p>
<p><a target="_blank" rel="noopener" href="http://www.fontawesome.com.cn/faicons/">fontawesome</a></p>
</blockquote>
<p>Iconfont 相较于 PNG 的优势：</p>
<ul>
<li><p>多个图标使用一套字体，减少获取时的请求数量和体积</p>
<p>因为网站会有很多图标，如果使用 PNG，每个图标都需要单独设计一个文件，这样浏览器就需要对每一个文件进行加载。虽然可以使用雪碧图来规避请求数量，但是这就需要关心 icon 的定位了</p>
<p>iconfont 就是一套字体，就只需要获取一套字体即可</p>
</li>
<li><p>矢量图形，可伸缩，可以直接通过 CSS 修改样式（颜色、大小等）</p>
<p>PNG 需要关注图片的宽度、比例，以避免失真、变形</p>
</li>
</ul>
<p>Iconfont  缺陷：</p>
<ul>
<li>Iconfont 很难做到多色</li>
<li>浏览器和搜索引擎很难理解这个字体图标代表什么意思</li>
</ul>
<p>这时人们就在想有没有什么方式类似 HTML，把这个图片描述出来，这样一方面可以显示图标，另一方面还能让搜索引擎理解这个代表什么意思。这时人们就把一项老技术 svg 翻出来了</p>
<h3 id="svg"><a href="#svg" class="headerlink" title="svg"></a>svg</h3><blockquote>
<p><a target="_blank" rel="noopener" href="https://juejin.cn/post/6844903517564436493">手摸手，带你优雅的使用 icon</a> 这里使用 <code>svg-sprite-loader</code> 对 svg 进行处理</p>
</blockquote>
<p>采用 <code>@svgr/webpack</code> 支持 svg 作为组件引用</p>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">npm install -D @svgr/webpack</span><br></pre></td></tr></table></figure>

<p>之后在 <code>webpack.config.js</code> 里配置即可</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">module</span>.exports = smp.wrap(&#123;</span><br><span class="line">  <span class="built_in">module</span>: &#123;</span><br><span class="line">    rules: [</span><br><span class="line">      &#123;</span><br><span class="line">        test: <span class="regexp">/\.svg$/</span>,</span><br><span class="line">        use: [<span class="string">&#x27;@svgr/webpack&#x27;</span>],</span><br><span class="line">      &#125;,</span><br><span class="line">    ],</span><br><span class="line">  &#125;,</span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure>

<p>在页面里直接使用</p>
<figure class="highlight jsx"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">About</span> <span class="keyword">extends</span> <span class="title">Component</span> </span>&#123;</span><br><span class="line">  <span class="function"><span class="title">render</span>(<span class="params"></span>)</span> &#123;</span><br><span class="line">    <span class="keyword">return</span> (</span><br><span class="line">      &lt;main className=&#123;<span class="built_in">this</span>.props.classes.root&#125;&gt;</span><br><span class="line">        &lt;AddressCardSvg width=&#123;<span class="number">100</span>&#125; color=&#123;<span class="string">&#x27;#fa1010&#x27;</span>&#125;/&gt;</span><br><span class="line">      &lt;/main&gt;</span><br><span class="line">    )</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><strong>svg优势：</strong></p>
<ul>
<li>保持了图片能力，支持色彩和复杂图标的绘制</li>
<li>独立的矢量图形，用哪个加载哪个</li>
<li>XML 语法，搜索引擎 SEO 和无障碍读屏软件读取</li>
</ul>
<h2 id="使用-Flexbox-布局"><a href="#使用-Flexbox-布局" class="headerlink" title="使用 Flexbox 布局"></a>使用 Flexbox 布局</h2><p>我们把一个元素的 <code>display: flex</code>，这个元素就会变成 flex 容器</p>
<p>flex 容器有如下属性：</p>
<ol>
<li>flex-direction：容器的主轴的方向</li>
<li>flex-wrap：是否换行</li>
<li>flex-flow：上面两个属性的简写</li>
<li>justify-content：主轴上的对齐方式</li>
<li>align-items：交叉轴上的对齐方式</li>
<li>align-content：多条轴的 flex 在交叉轴的对齐</li>
</ol>
<p>子元素有如下属性：</p>
<ol>
<li>order：排列时的顺序</li>
<li>flex-grow：宽度或长度的增长系数（容器空间多大时）</li>
<li>flex-shrink：缩小系数（容器空间不足时）</li>
<li>flex-basis：主轴方向上的初始大小</li>
<li>flex：2、3、4 的简写方式</li>
<li>align-self：交叉轴上的排列方向</li>
</ol>
<h3 id="float-与-flexbox-进行对比"><a href="#float-与-flexbox-进行对比" class="headerlink" title="float 与 flexbox 进行对比"></a>float 与 flexbox 进行对比</h3><p><strong>使用 float 进行布局</strong></p>
<ul>
<li><code>display: inline-block</code>：进行换行会 <code>float: left</code> 要快，但也没有 <code>dispaly: flex</code> 快</li>
</ul>
<p><img data-src="https://gitee.com/lilyn/pic/raw/master/jslearn-img/202203141005322.png"></p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">style</span>&gt;</span></span><br><span class="line"><span class="css">    <span class="selector-class">.main</span> &#123;</span></span><br><span class="line">      width: 100%;</span><br><span class="line">      height: 1000px;</span><br><span class="line">      background-color: gray;</span><br><span class="line">    &#125;</span><br><span class="line"><span class="css">    <span class="selector-class">.box</span> &#123;</span></span><br><span class="line">      width: 100px;</span><br><span class="line">      height: 100px;</span><br><span class="line">      background-color: red;</span><br><span class="line">      margin: 5px;</span><br><span class="line">      float: left;</span><br><span class="line">    &#125;</span><br><span class="line">  <span class="tag">&lt;/<span class="name">style</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">&quot;main&quot;</span> <span class="attr">class</span>=<span class="string">&quot;main&quot;</span>&gt;</span><span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="javascript">  <span class="built_in">window</span>.addEventListener(<span class="string">&#x27;load&#x27;</span>, <span class="function">() =&gt;</span> &#123;</span></span><br><span class="line"><span class="javascript">    <span class="keyword">let</span> mainNode = <span class="built_in">document</span>.getElementById(<span class="string">&#x27;main&#x27;</span>)</span></span><br><span class="line"><span class="javascript">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="number">100000</span>; i++) &#123;</span></span><br><span class="line"><span class="javascript">      <span class="keyword">let</span> divNode = <span class="built_in">document</span>.createElement(<span class="string">&#x27;div&#x27;</span>)</span></span><br><span class="line"><span class="javascript">      divNode.setAttribute(<span class="string">&#x27;class&#x27;</span>, <span class="string">&#x27;box&#x27;</span>)</span></span><br><span class="line">      mainNode.appendChild(divNode)</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;)</span><br><span class="line"><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p><strong>使用 Flexbox 进行布局</strong></p>
<p><img data-src="https://gitee.com/lilyn/pic/raw/master/jslearn-img/202203141009448.png"></p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">style</span>&gt;</span></span><br><span class="line"><span class="css">    <span class="selector-class">.main</span> &#123;</span></span><br><span class="line">      width: 100%;</span><br><span class="line">      height: 1000px;</span><br><span class="line">      background-color: gray;</span><br><span class="line">      display: flex;</span><br><span class="line">      flex-flow: row wrap;</span><br><span class="line">    &#125;</span><br><span class="line"><span class="css">    <span class="selector-class">.box</span> &#123;</span></span><br><span class="line">      width: 100px;</span><br><span class="line">      height: 100px;</span><br><span class="line">      background-color: red;</span><br><span class="line">      margin: 5px;</span><br><span class="line">    &#125;</span><br><span class="line">  <span class="tag">&lt;/<span class="name">style</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">&quot;main&quot;</span> <span class="attr">class</span>=<span class="string">&quot;main&quot;</span>&gt;</span><span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="javascript">  <span class="built_in">window</span>.addEventListener(<span class="string">&#x27;load&#x27;</span>, <span class="function">() =&gt;</span> &#123;</span></span><br><span class="line"><span class="javascript">    <span class="keyword">let</span> mainNode = <span class="built_in">document</span>.getElementById(<span class="string">&#x27;main&#x27;</span>)</span></span><br><span class="line"><span class="javascript">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="number">100000</span>; i++) &#123;</span></span><br><span class="line"><span class="javascript">      <span class="keyword">let</span> divNode = <span class="built_in">document</span>.createElement(<span class="string">&#x27;div&#x27;</span>)</span></span><br><span class="line"><span class="javascript">      divNode.setAttribute(<span class="string">&#x27;class&#x27;</span>, <span class="string">&#x27;box&#x27;</span>)</span></span><br><span class="line">      mainNode.appendChild(divNode)</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;)</span><br><span class="line"><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br></pre></td></tr></table></figure>

<h3 id="Flexbox-优势"><a href="#Flexbox-优势" class="headerlink" title="Flexbox 优势"></a>Flexbox 优势</h3><ul>
<li>更好性能的实现方案：使用 Flexbox 布局在 Layout 和 Paint 耗时小于其他布局方式</li>
<li>容器可以决定子元素的几何属性：大小、顺序、对齐方式、间隔等</li>
<li>双向布局</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">style</span>&gt;</span></span><br><span class="line"><span class="css">    <span class="selector-class">.flex-container</span> &#123;</span></span><br><span class="line">      display: flex;</span><br><span class="line">      flex-flow: row wrap;</span><br><span class="line">      justify-content: space-around;</span><br><span class="line">    &#125;</span><br><span class="line"><span class="css">    <span class="selector-class">.flex-card</span> &#123;</span></span><br><span class="line">      width: 200px;</span><br><span class="line">      height: 200px;</span><br><span class="line">      display: flex;</span><br><span class="line">      justify-content: center;</span><br><span class="line">      align-items: center;</span><br><span class="line">    &#125;</span><br><span class="line"><span class="css">    <span class="selector-class">.flex-card-number</span> &#123;</span></span><br><span class="line">      font-size: 120px;</span><br><span class="line">      color: white;</span><br><span class="line">    &#125;</span><br><span class="line">  <span class="tag">&lt;/<span class="name">style</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">div</span> <span class="attr">id</span>=<span class="string">&quot;flex-container&quot;</span> <span class="attr">class</span>=<span class="string">&quot;flex-container&quot;</span>&gt;</span><span class="tag">&lt;/<span class="name">div</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">script</span>&gt;</span></span><br><span class="line"><span class="javascript">  <span class="function"><span class="keyword">function</span> <span class="title">generateRandomColor</span>(<span class="params"></span>) </span>&#123;</span></span><br><span class="line"><span class="javascript">    <span class="keyword">let</span> r = <span class="built_in">Math</span>.floor(<span class="built_in">Math</span>.random() * <span class="number">256</span>)</span></span><br><span class="line"><span class="javascript">    <span class="keyword">let</span> g = <span class="built_in">Math</span>.floor(<span class="built_in">Math</span>.random() * <span class="number">256</span>)</span></span><br><span class="line"><span class="javascript">    <span class="keyword">let</span> b = <span class="built_in">Math</span>.floor(<span class="built_in">Math</span>.random() * <span class="number">256</span>)</span></span><br><span class="line"><span class="javascript">    <span class="keyword">return</span> <span class="string">&#x27;rgb(&#x27;</span> + r + <span class="string">&#x27;,&#x27;</span> + g + <span class="string">&#x27;,&#x27;</span> + b + <span class="string">&#x27;)&#x27;</span></span></span><br><span class="line">  &#125;</span><br><span class="line"><span class="javascript">  <span class="built_in">window</span>.addEventListener(<span class="string">&#x27;load&#x27;</span>, <span class="function">() =&gt;</span> &#123;</span></span><br><span class="line"><span class="javascript">    <span class="keyword">let</span> containerNode = <span class="built_in">document</span>.getElementById(<span class="string">&#x27;flex-container&#x27;</span>)</span></span><br><span class="line"><span class="javascript">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="number">10</span>; i++) &#123;</span></span><br><span class="line"><span class="javascript">      <span class="keyword">let</span> divNode = <span class="built_in">document</span>.createElement(<span class="string">&#x27;div&#x27;</span>)</span></span><br><span class="line"><span class="javascript">      divNode.setAttribute(<span class="string">&#x27;class&#x27;</span>, <span class="string">&#x27;flex-card&#x27;</span>)</span></span><br><span class="line">      divNode.style.backgroundColor = generateRandomColor()</span><br><span class="line"><span class="javascript">      <span class="keyword">let</span> spanNode = <span class="built_in">document</span>.createElement(<span class="string">&#x27;span&#x27;</span>)</span></span><br><span class="line"><span class="javascript">      spanNode.setAttribute(<span class="string">&#x27;class&#x27;</span>, <span class="string">&#x27;flex-card-number&#x27;</span>)</span></span><br><span class="line"><span class="javascript">      spanNode.appendChild(<span class="built_in">document</span>.createTextNode((i + <span class="number">1</span>).toString()))</span></span><br><span class="line">      divNode.appendChild(spanNode)</span><br><span class="line">      containerNode.appendChild(divNode)</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;)</span><br><span class="line"><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br></pre></td></tr></table></figure>

<h2 id="优化资源加载顺序"><a href="#优化资源加载顺序" class="headerlink" title="优化资源加载顺序"></a>优化资源加载顺序</h2><blockquote>
<p><a target="_blank" rel="noopener" href="https://zhuanlan.zhihu.com/p/30558018">从Chrome源码看浏览器如何加载资源</a></p>
</blockquote>
<p>使用 Preload 和 Prefetch 改变浏览器默认的资源加载优先级</p>
<ul>
<li><p>Preload：提前加载较晚出现，但对当前页面非常重要的资源</p>
<p>字体比较特殊，需要设置 <code>crossorigin=&quot;anonymous&quot;</code></p>
</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">link</span> <span class="attr">rel</span>=<span class="string">&quot;preload&quot;</span> <span class="attr">href</span>=<span class="string">&quot;test.jpg&quot;</span> <span class="attr">as</span>=<span class="string">&quot;font&quot;</span> /&gt;</span></span><br><span class="line"></span><br><span class="line">&lt;link</span><br><span class="line">  rel=&quot;preload&quot;</span><br><span class="line">  href=&quot;https://fonts.gstatic.com/s/longcang/v15/LYjAdGP8kkgoTec8zkRgqBgxXsWsMfnCm1_q1j3gcsptb8OMg_Z2HVZhDbPBCIyx.119.woff2&quot;</span><br><span class="line">  as=&quot;font&quot;</span><br><span class="line">  type=&quot;font/woff2&quot;</span><br><span class="line">  crossorigin=&quot;anonymous&quot;</span><br><span class="line">/&gt;</span><br></pre></td></tr></table></figure>

<ul>
<li>Prefetch：提前加载后续页面或后续路由所需的资源，优先级低</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">link</span> <span class="attr">rel</span>=<span class="string">&quot;prefetch&quot;</span> <span class="attr">as</span>=<span class="string">&quot;style&quot;</span> <span class="attr">href</span>=<span class="string">&quot;product-font.css&quot;</span> /&gt;</span></span><br></pre></td></tr></table></figure>

<p><img data-src="https://gitee.com/lilyn/pic/raw/master/jslearn-img/202203141704726.png"></p>
<p>对于那些在当前页面使用的资源可以利用 Preload，而对一些可能在将来某些页面中使用的资源可以利用 Prefetch。从加载优先级上看，Preload 会提升请求优先级，而 Prefetch 会把资源的优先级防止最低，当浏览器空闲时采取加载</p>
<blockquote>
<p><a target="_blank" rel="noopener" href="https://webpack.js.org/guides/code-splitting/#prefetchingpreloading-modules">prefetchingpreloading-modules</a></p>
</blockquote>
<p>webpack 提前预加载处理，只需要加上一行注释</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span>(<span class="comment">/* webpackPrefetch: true */</span> <span class="string">&#x27;./path/to/LoginModal.js&#x27;</span>)</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span>(<span class="comment">/* webpackPreload: true */</span> <span class="string">&#x27;ChartingLibrary&#x27;</span>)</span><br></pre></td></tr></table></figure>

<h2 id="预渲染页"><a href="#预渲染页" class="headerlink" title="预渲染页"></a>预渲染页</h2><blockquote>
<p><a target="_blank" rel="noopener" href="https://github.com/stereobooster/react-snap">react-snap</a></p>
<p><a target="_blank" rel="noopener" href="https://awesome-vue.js.org/components-and-libraries/prerendering.html">Awesome Prerendering</a></p>
<p><a target="_blank" rel="noopener" href="https://juejin.cn/post/6844903668488093704">Vue项目预渲染机制引入实践</a></p>
<p><a target="_blank" rel="noopener" href="https://blog.csdn.net/weixin_44524835/article/details/110221911">Vue实现预渲染</a></p>
</blockquote>
<p>SEO 为什么对 SPA 不友好</p>
<ol>
<li>爬虫在爬去页面时，不会去执行 JS，所以隐藏在 JS 中的跳转不会获取到</li>
<li>加载页面时，浏览器的渲染包括：Html 解析、Dom 树构建、Cssom 树构建、JavaScript 解析、布局、绘制，当解析到 JavaScript 时才会去触发 Vue 渲染，然后元素挂载上去，所以即使 vue 渲染机制很快我们仍然需要看到一段时间白屏</li>
</ol>
<p><strong>服务端渲染（Server Side Rendering）</strong> 可以用于 SEO 优化，但其牺牲了 TTFB 来补救首屏渲染，即使有 Next.js等技术，SSR 实现起来还是比较复杂。这里还有一种解决方案，就是<strong>预渲染（Prerending）</strong></p>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">npm install -D react-snap</span><br></pre></td></tr></table></figure>

<p>在 <code>package.json</code> 中增加一条 scipts，这里可以通过 npm 一个钩子函数，在 build 完成后，自动触发 postbuild</p>
<figure class="highlight json"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">&#123;</span><br><span class="line">  <span class="attr">&quot;scripts&quot;</span>: &#123;</span><br><span class="line">    <span class="attr">&quot;build&quot;</span>: <span class="string">&quot;cross-env NODE_ENV=production webpack&quot;</span>,</span><br><span class="line">    <span class="attr">&quot;postbuild&quot;</span>: <span class="string">&quot;react-snap&quot;</span></span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>如果使用 React 做 SSR，它会对页面渲染进行修改，通常使用 <code>ReactDOM.render</code>，对主节点上相关元素进行渲染，如果主节点已经有元素了，就不需要触发 <code>ReactDOM.render</code></p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> root = <span class="built_in">document</span>.getElementById(<span class="string">&#x27;main&#x27;</span>)</span><br><span class="line"></span><br><span class="line"><span class="keyword">if</span> (root.hasChildNodes()) &#123;</span><br><span class="line">  ReactDOM.hydrate(<span class="xml"><span class="tag">&lt;<span class="name">App</span> /&gt;</span></span>, root)</span><br><span class="line">&#125; <span class="keyword">else</span> &#123;</span><br><span class="line">  ReactDOM.render(<span class="xml"><span class="tag">&lt;<span class="name">App</span> /&gt;</span></span>, root)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>Vue 中使用只配置 <code>package.json</code> 即可</p>
<figure class="highlight json"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">&#123;</span><br><span class="line">  <span class="attr">&quot;scripts&quot;</span>: &#123;</span><br><span class="line">    <span class="attr">&quot;postbuild&quot;</span>: <span class="string">&quot;react-snap&quot;</span></span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="attr">&quot;reactSnap&quot;</span>: &#123;</span><br><span class="line">    <span class="attr">&quot;source&quot;</span>: <span class="string">&quot;dist&quot;</span>,</span><br><span class="line">    <span class="attr">&quot;inlineCss&quot;</span>: <span class="literal">true</span>, <span class="comment">// 内联样式，避免明显的样式闪动</span></span><br><span class="line">    <span class="attr">&quot;minifyHtml&quot;</span>: &#123;</span><br><span class="line">      <span class="attr">&quot;collapseWhitespace&quot;</span>: <span class="literal">false</span>,</span><br><span class="line">      <span class="attr">&quot;removeComments&quot;</span>: <span class="literal">false</span></span><br><span class="line">    &#125;</span><br><span class="line">  &#125;,</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>预渲染的作用：</p>
<ul>
<li>大型单页应用的性能瓶颈：<strong>JS 下载 + 解析 + 执行</strong></li>
<li>SSR 主要问题：牺牲 <strong>TTFB</strong> 来补救 <strong>First Paint</strong>，<strong>实现复杂</strong></li>
<li>Pre-rendering 打包时提前渲染页面，没有服务端参与</li>
</ul>
<h2 id="Windowing（窗口化）提高列表性能"><a href="#Windowing（窗口化）提高列表性能" class="headerlink" title="Windowing（窗口化）提高列表性能"></a>Windowing（窗口化）提高列表性能</h2><p><img data-src="https://gitee.com/lilyn/pic/raw/master/jslearn-img/202203151034771.png"></p>
<blockquote>
<p><a target="_blank" rel="noopener" href="https://bvaughn.github.io/forward-js-2017/#/13/5">What can windowing be used for</a></p>
</blockquote>
<ul>
<li><p>Tables, lists, spreadsheets (<a target="_blank" rel="noopener" href="https://github.com/bvaughn/react-virtualized">react-virtualized</a>)</p>
<p><img data-src="https://gitee.com/lilyn/pic/raw/master/jslearn-img/202203151041604.gif"></p>
</li>
<li><p>Drop-down menus (<a target="_blank" rel="noopener" href="https://github.com/bvaughn/react-virtualized-select">react-virtualized-select</a>)</p>
<p><img data-src="https://gitee.com/lilyn/pic/raw/master/jslearn-img/202203151040676.gif"></p>
</li>
</ul>
<p>安装：</p>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">npm i -D react-window</span><br></pre></td></tr></table></figure>

<p>使用：</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> &#123; FixedSizeGrid, FixedSizeList &#125; <span class="keyword">from</span> <span class="string">&#x27;react-window&#x27;</span></span><br><span class="line"><span class="keyword">import</span> model <span class="keyword">from</span> <span class="string">&#x27;./model&#x27;</span></span><br><span class="line"><span class="keyword">import</span> React <span class="keyword">from</span> <span class="string">&#x27;react&#x27;</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> items = []</span><br><span class="line"></span><br><span class="line"><span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="number">100</span>; i++) &#123;</span><br><span class="line">  items.push(model.map(<span class="function"><span class="params">m</span> =&gt;</span> <span class="xml"><span class="tag">&lt;<span class="name">img</span> <span class="attr">src</span>=<span class="string">&#123;m.image&#125;</span> <span class="attr">alt</span>=<span class="string">&#123;m.name&#125;</span> <span class="attr">width</span>=<span class="string">&#123;100&#125;</span> <span class="attr">height</span>=<span class="string">&#123;90&#125;</span> /&gt;</span></span>))</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">const</span> Row = <span class="function">(<span class="params">&#123; index, style &#125;</span>) =&gt;</span> &#123;</span><br><span class="line">  <span class="keyword">let</span> styleExt = &#123;</span><br><span class="line">    ...style,</span><br><span class="line">    borderBottom: <span class="string">&#x27;1px solid #fff&#x27;</span>,</span><br><span class="line">    display: <span class="string">&#x27;flex&#x27;</span>,</span><br><span class="line">    alignItems: <span class="string">&#x27;center&#x27;</span>,</span><br><span class="line">    justifyContent: <span class="string">&#x27;center&#x27;</span>,</span><br><span class="line">  &#125;</span><br><span class="line">  <span class="keyword">return</span> <span class="xml"><span class="tag">&lt;<span class="name">div</span> <span class="attr">style</span>=<span class="string">&#123;styleExt&#125;</span>&gt;</span>&#123;items[index]&#125;<span class="tag">&lt;/<span class="name">div</span>&gt;</span></span></span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">ListComponent</span> <span class="keyword">extends</span> <span class="title">React</span>.<span class="title">Component</span> </span>&#123;</span><br><span class="line">  listRef = React.createRef()</span><br><span class="line"></span><br><span class="line">  scrollToRow = <span class="function"><span class="params">rowNum</span> =&gt;</span> <span class="function">() =&gt;</span> &#123;</span><br><span class="line">    <span class="keyword">if</span> (rowNum &lt;= <span class="number">0</span> || rowNum &gt; items.length) <span class="keyword">return</span></span><br><span class="line">    <span class="built_in">this</span>.listRef.current.scrollToItem(rowNum)</span><br><span class="line">  &#125;</span><br><span class="line"></span><br><span class="line">  <span class="function"><span class="title">render</span>(<span class="params"></span>)</span> &#123;</span><br><span class="line">    <span class="keyword">return</span> (</span><br><span class="line">      &lt;div&gt;</span><br><span class="line">        &lt;button onClick=&#123;<span class="built_in">this</span>.scrollToRow(<span class="number">50</span>)&#125;&gt;Scroll&lt;/button&gt;</span><br><span class="line">		<span class="comment">/* 一维列表List */</span></span><br><span class="line">        &lt;FixedSizeList</span><br><span class="line">          ref=&#123;<span class="built_in">this</span>.listRef&#125;</span><br><span class="line">          height=&#123;<span class="number">360</span>&#125;</span><br><span class="line">          width=&#123;<span class="number">400</span>&#125;</span><br><span class="line">          itemSize=&#123;<span class="number">120</span>&#125;</span><br><span class="line">          itemCount=&#123;items.length&#125;</span><br><span class="line">          className=&#123;<span class="built_in">this</span>.props.className&#125;</span><br><span class="line">        &gt;</span><br><span class="line">          &#123;Row&#125;</span><br><span class="line">        &lt;/FixedSizeList&gt;</span><br><span class="line">		<span class="comment">/* 二维列表Grid */</span></span><br><span class="line">        &#123;<span class="comment">/* &lt;FixedSizeGrid</span></span><br><span class="line"><span class="comment">          columnCount=&#123;1000&#125;</span></span><br><span class="line"><span class="comment">          columnWidth=&#123;100&#125;</span></span><br><span class="line"><span class="comment">          height=&#123;150&#125;</span></span><br><span class="line"><span class="comment">          rowCount=&#123;1000&#125;</span></span><br><span class="line"><span class="comment">          rowHeight=&#123;35&#125;</span></span><br><span class="line"><span class="comment">          width=&#123;300&#125;</span></span><br><span class="line"><span class="comment">        &gt;</span></span><br><span class="line"><span class="comment">          &#123;Row&#125;</span></span><br><span class="line"><span class="comment">        &lt;/FixedSizeGrid&gt; */</span>&#125;</span><br><span class="line">      &lt;/div&gt;</span><br><span class="line">    )</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">export</span> <span class="keyword">default</span> ListComponent</span><br></pre></td></tr></table></figure>

<p>windowing 的作用：</p>
<ul>
<li>加载大列表、大表单的每一行严重影响性能</li>
<li>Lazy loading 仍然会让 DOM 变得过大</li>
<li>windowing 只渲染可见的行，渲染和滚动的性能都会提升</li>
</ul>
<h2 id="使用骨架组件减少布局移动（Layout-Shift）"><a href="#使用骨架组件减少布局移动（Layout-Shift）" class="headerlink" title="使用骨架组件减少布局移动（Layout Shift）"></a>使用骨架组件减少布局移动（Layout Shift）</h2><p>当相关组件数据还没有完全加载时，如果样式没有控制好，会导致组件没有完全撑开，当样式加载好之后，组件的布局会发生变化，对周围的组件也会造成影响，这个性能消耗比较高，我们应该尽量避免</p>
<p>骨架组件也叫 Skeleton 或 Placeholder（占位符），用来占位和提升用户感知，可以在 Google DevTools 里键入 <code>ctrl + shift + p</code>，输入 <code>Layout Shift Regions</code></p>
<ul>
<li>安装</li>
</ul>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">npm i -D react-placeholder</span><br></pre></td></tr></table></figure>

<ul>
<li>使用</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> ReactPlaceholder <span class="keyword">from</span> <span class="string">&#x27;react-placeholder&#x27;</span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Contact</span> <span class="keyword">extends</span> <span class="title">Component</span> </span>&#123;</span><br><span class="line">  <span class="function"><span class="title">render</span>(<span class="params"></span>)</span> &#123;</span><br><span class="line">    <span class="keyword">const</span> &#123; ready &#125; = <span class="built_in">this</span>.state</span><br><span class="line">    <span class="keyword">const</span> imageStyle = !ready ? &#123; <span class="attr">display</span>: <span class="string">&#x27;none&#x27;</span> &#125; : &#123;&#125;</span><br><span class="line">    <span class="keyword">let</span> cardMedia = (</span><br><span class="line">      &lt;CardMedia</span><br><span class="line">        component=&#123;<span class="string">&#x27;img&#x27;</span>&#125;</span><br><span class="line">        style=&#123;imageStyle&#125;</span><br><span class="line">        className=&#123;<span class="built_in">this</span>.props.classes.media&#125;</span><br><span class="line">        image=&#123;<span class="built_in">this</span>.props.image&#125;</span><br><span class="line">        onLoad=&#123;<span class="built_in">this</span>.becomeReady&#125;</span><br><span class="line">      /&gt;</span><br><span class="line">    )</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> (</span><br><span class="line">      &lt;div className=&#123;<span class="built_in">this</span>.props.classes.root&#125;&gt;</span><br><span class="line">        &lt;ReactPlaceholder ready=&#123;<span class="built_in">this</span>.state.ready&#125; customPlaceholder=&#123;<span class="xml"><span class="tag">&lt;<span class="name">ContactPlaceholder</span> /&gt;</span></span>&#125;&gt;</span><br><span class="line">          <span class="comment">/* ... */</span></span><br><span class="line">        &lt;/ReactPlaceholder&gt;</span><br><span class="line">        &#123;!ready &amp;&amp; cardMedia&#125;</span><br><span class="line">      &lt;/div&gt;</span><br><span class="line">    )</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>


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